This invention relates to an optical fiber service cable. The cable may serve as a buried service cable in a local area network to extend from the outdoor environment to customer premises.
Optical service cables, sometimes called drop cables, must differ somewhat in design from typical indoor cables and outdoor cables in that they must be operable both in the outdoor environment, where the optical fibers must be protected from deleterious effects resulting from water ingress, and the indoor environment, in which the cable must pass tests to ensure that it does not rapidly spread flames from one part of the building to another through a riser duct. The UL-1666 vertical flame test is commonly used for this purpose. The fluid waterblocking compositions often used in cables for outdoor applications must be compensated for in order for a cable to pass the required flame test. A service cable designed to meet these problems is U.S. Pat. No. 4,892,282 which issued on Jan. 9, 1990 in the names of Christopher A. Story and Susan M. Cooper. The Story et al. cable includes a core tube made of a flame-resistant material such as a thermoplastic rubber enclosing individual coated optical fibers and a filling compound. The core tube is surrounded by a tensile layer of densely packed loose fiberglass yarns, and water swellable powder may be applied thereover. A layer of fiber reinforced plastic members for compressive strength surrounds the loose fiberglass yarn layer, and is enclosed in a sheath of flame-resistant material.
Another service cable is disclosed in U.S. Pat. No. 5,050,957, which also provides a flame-retardant outer sheath, a core tube holding individual coated optical fibers, and a strength member system between the sheath and the core tube. Waterblocking yarns are also present. An alternate embodiment includes a waterblocking tape and a metallic tape layer.
U.S. Pat. No. 5,343,549, which issued Aug. 30, 1994 in the names of Samuel D. Nave and Harvey R. McDowell, III, includes an outer flame resistant jacket over multiple layers of buffer tubes containing individual optical fibers and filling compound which are stranded about a central tensile member. Between the outer buffer tube layer and the outer jacket is a system including a flame resistant tape between layers of aramid yarns.
Optical fiber ribbon cables are also used in today's telecommunication networks. Ribbon cables are sometimes thought to be desirable, especially where it is important to gang splice many optical fiber connections in a short time. U.S. Pat. No. 5,293,443, which issued Mar. 8, 1994 in the names of Christopher K. Eoll et al. discloses an optical fiber cable having buffer tubes stranded around a central member, the buffer tubes holding optical ribbons and a filling compound. The Eoll et al. cable is not disclosed to be suitable for an indoor environment and does not disclose flame retardance as an object of the cable.
What is desired and seemingly is not provided by the prior art is an optical fiber ribbon service cable including both flame retardance and waterblocking provisions. The prior art also seemingly has not provided filling compounds including flame-retardant materials in optical service cables.